Abstract

Maximum values for the single-domain threshold d0 and superpara-magnetic threshold d8 in pure magnetite are found to be 570±50 and 350±50 angstroms, respectively. Particles larger than do but smaller than about 0.25 micron have size-dependent saturation remanences and coercive forces like those of multidomain particles, but intense and stable thermoremanent magnetization like that of single-domain particles. The presence of magnetite grains in this size range could account for the essentially single-domain character of stable natural remanence in many volcanic and intrusive rocks.